1. Field of the Invention
The present invention relates to wireless communication apparatus and a multi-hop communication method that uses source routing.
2. Description of the Related Art
A multi-hop communication method using source routing is described in the ZigBee Specification, Document 053474r17. When a packet is transmitted, the source node adds a header listing the addresses of all the nodes on the relay path to the destination node (see Section 3.6.3.3.1 of the ZigBee Specification). Each node that relays the packet increments an index value in the header that indicates the next relay node in the address list (Section 3.6.3.3.2). The route is originally established by transmission of a route record packet from the destination node to the source node. Each node that relays the route record packet adds its own address to the address list (Section 3.6.3.5.4), enabling the source node to identify the route by which the route record packet arrived from the destination node.
Source routing enables multi-hop communication to be carried out without storing and maintaining routing tables at the relay nodes. Memory and processing power requirements at the relay nodes are thereby reduced, conserving energy and permitting the use of low-cost processors.
Source routing is problematic, however, in that the header of every packet must include the addresses of all the relay nodes from the source node to the destination node. As the number of relay hops increases, the size of the header increases and the payload data size must be reduced accordingly. The ZigBee specification is based on a standard (IEEE 802.15.4) that sets a maximum size of 128 bytes per packet, so when there are many hops, the address list overhead occupies a large part of each packet. More packets must then be used to transmit a given amount of information, consuming extra power and delaying processing of the information in software layers above the network layer.
There is a particular need for a more effective method of transmitting a consecutive series of packets to the same destination node, without transmitting the same address list repeatedly in the header information.